Volatile memory devices are used in many types of systems to provide relatively high-speed access of data. Typically, volatile memory devices include dynamic random access memories (DRAMs) and static random access memories (SRAMs). Volatile memory devices are commonly used in cache memories to temporarily store data that exists in secondary storage (e.g., hard disk drives).
With volatile memory devices, system power loss may cause loss of data stored in the volatile memory devices (that have not yet been written back to persistent secondary storage). To store certain critical data, some systems use battery-backed volatile memory devices. A battery-backed volatile memory device is a memory device that is coupled to a battery power source. In case of system power loss, power from the battery power source can be used to maintain data stored in the volatile memory device for some period of time (until the battery power source becomes depleted).
An issue associated with using batteries to provide backup power to volatile memory devices is that batteries are associated with a relatively short life. Batteries tolerate a fixed number of charge-discharge cycles before the batteries wear out, which may result in the batteries having to be replaced. Replacing batteries is associated with replacement costs that include part costs, service costs, and warranty costs. Also, relatively complex monitoring circuitry is often used to monitor a battery to ensure the battery has sufficient power to maintain data in a volatile memory device for a desired amount of time. Moreover, system design complexity is increased since the system has to be designed such that the battery can be accessed for replacement. In addition, worn out batteries have to be disposed, which is associated with disposal costs and which poses environmental concerns.